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By coordinating energy use for electricity, heating, and transportation, four Japanese cities plan to reduce their carbon footprints and increase reliance on renewables. The cities are pledging to cut their carbon-dioxide emissions by up to 40 percent by 2030, employing systems that will go beyond smart-grid proposals like those being implemented in the U.S. and elsewhere. While smart-grid projects manage electricity, the Japanese "smart community" demonstration projects will also manage energy for heating and transportation, said Hironori Nakanishi, a director at Japan's Ministry of Economy, Trade, and Industry, describing the projects at a recent smart-grid conference in Gaithersburg, Maryland.

The projects, which got under way this year, were instigated by the Japanese government in part to fulfill a pledge the prime minister made last year to reduce greenhouse gas emissions by 25 percent by 2020. They will cost about $1 billion over five years and are being implemented by consortia of dozens of companies including Toyota, Nissan, Nippon Steel, and Panasonic.

Achieving the emissions goal, Nakanishi said, will require installing some 28 gigawatts of solar power, the equivalent of about 28 large nuclear reactors. Smart-grid technology will help grid operators accommodate large amounts of electricity from solar and other renewable energy sources: as clouds pass overhead or wind patterns change, for example, signals could be sent out to smart appliances to pause operation or decrease their power consumption. In a smart community, this adaptability would be augmented by also managing heat. "More than half of energy is used as heat, so the integration of heat and electricity is quite important," Nakanishi said.

Panasonic already makes a system that integrates the two at the level of an individual home. It pairs a fuel cell system that generates electricity and heat from natural gas with an extremely efficient solar power array and a battery to store excess power from the solar panels. Such a system, which costs about $60,000, can make a single home independent from the grid, Nakanishi said. In the future, an electric vehicle that can store electricity might be added to such a system.

When the sun is shining, the solar panels power the home. Excess electricity is used to heat water, and it could charge the car's battery. When it's cloudy, and at night, the system relies on stored electricity and the natural gas fuel cell system. Heat produced by the fuel cells, which ordinarily would be wasted, helps heat the home, reducing total energy consumption. The system can be optimized by installing DC as well as AC power outlets, because solar panels produce, and batteries deliver, DC, and some appliances, such as computers and certain TVs, can run on it.

The details of the systems vary among the four demonstration projects. At Toyota City and Yokohama, thousands of electric cars from Toyota and Nissan, respectively, will be integrated into the grid; the cars will be able to store extra renewable energy and deliver power back to the grid when energy production drops. At Kitakyushu, the emphasis will be on hydrogen fuel cells, in part because Nippon Steel already manages large amounts ofhydrogen fuel. Kansai Science City will emphasize new software that allows consumers to see and manage their energy use, though its system will also incorporate electric vehicles and photovoltaics.